1. Field of the Invention
The present invention relates to a technique of inspecting patterns such as photomask patterns formed on a sample used to fabricate semiconductor devices or liquid-crystal display (LCD) devices, or patterns formed on a sample such as a semiconductor or LCD device, to see if the patterns are sound without faults. In particular, the present invention relates to pattern inspection equipment, a pattern inspection method, and a computer-readable storage medium storing a pattern inspection program, for realizing such a technique.
2. Description of the Related Art
Large-scale integrated circuits (LSIs) are manufactured with the use of photolithography and photomasks. The yields of LSIs becomes poor if patterns of the photomasks have faults. Then, various kinds of equipment have been developed to inspect the faults in the photomask patterns.
Photomask patterns are formed by depositing a metal film such as a chrome film on a glass substrate, coating the metal film with photoresist, exposing, developing, and baking them, and etching the metal film with the photoresist as a mask. The etching may be wet etching, dry etching, or any other. According to the etching conditions, the undercuts, sidewall angles, anisotropy, pattern transformation of the metal film vary. The photomask patterns may have rounded corners depending on the photoresist exposing conditions and the metal film etching conditions. Then, an optical image taken from the actual photomask patterns generated on the glass substrate does not correctly match with designed patterns. Namely, the sizes, line widths, and edge positions of the actual photomask patterns slightly differ from those of the designed patterns serving as a reference to inspect the actual photomask patterns because the actual photomask patterns involve edge displacement and corner roundness while the designed patterns involve none of them.
As a result, the pattern inspection equipment frequently determines that the photomask patterns are defective even if they are substantially homothetic transformation of the designed patterns. And, if designed patterns are used as they are to inspect actual patterns, they will lead to erroneous results determining that the actual patterns have rounded corners and are defective, even if they are substantially same geometry as the designed patterns.
FIG. 1 shows pattern inspection equipment according to a prior art to cope with the situation that the actual photomask patterns can have slightly displaced edges. This equipment develops design data into pattern data and modifies the pattern data to adjust it to match with actual photomask patterns. The size-modified pattern data is used as reference data, which is compared with measured pattern data taken from the actual photomask patterns. A light source 2 emits light to irradiate a photomask 1 having patterns delineated according to the design data. The light passes through the photomask 1 and an object lens 4 and forms an optical image of the photomask patterns on a sensor 3. A sensor circuit 5 measures the image, digitizes it into measured pattern data, and transfers it to a fault decision circuit 6. Even if the actual photomask patterns have sharp edges, the measured pattern data does not provide perfect rectangular waveforms because the measured pattern data involves a blur produced by the optical observation system. Namely, the measured pattern data involves blurred edges.
On the other hand, a CPU 9 in a host computer system transfers the design data from a data memory to a binary pattern development circuit 8, which develops the design data into binary data made of xe2x80x9c1sxe2x80x9d and xe2x80x9c0sxe2x80x9d. The binary data is sent to a size modification circuit 7, which adjusts the binary data to match with changes in the photomask patterns caused by mask manufacturing processes. The adjusted pattern data is sent to the fault decision circuit 6. A front stage of the fault decision circuit 6 carries out a convolution process on the resized pattern data, to correct it for the blur of the measured pattern data caused by the observation optical system. A rear stage of the fault decision circuit 6 compares the adjusted, convoluted pattern data with the measured pattern data, to see if the photomask patterns have faults.
The size modification process carried out by the size modification circuit 7 will be explained. The design data used to delineate the photomask patterns is developed by the binary pattern development circuit 8 into binary data consisting of xe2x80x9c1sxe2x80x9d and xe2x80x9c0sxe2x80x9d. FIG. 2A shows an array 15 of xe2x80x9cnxc3x97nxe2x80x9d pixels in the binary data. The size modification circuit 7 calculates an OR of xe2x80x9c1sxe2x80x9d and xe2x80x9c0sxe2x80x9d in peripheral pixels 21 of the array 15. According to the OR, the size modification circuit 7 corrects a value at central pixel 22 of the array 15 to 1 or 0, thereby adjusting the sizes and line widths of the binary data to match with those of the actual photomask patterns. The fault decision circuit 6 compares the corrected pattern data with the measured pattern data, to see if the photomask patterns have faults.
The size of a sensor element (sensor pixel) of the sensor 3 is usually equal to the size of a pixel of the pattern data, and the size modification process is carried out pixel by pixel. As a result, the adjustment of design data to match with actual photomask patterns is restricted by the pixel size, and if a pattern edge is displaced by half a pixel size, the pattern inspection equipment will detect it as a fault. To avoid this type of erroneous detection, the equipment of the prior art must lower a threshold to determine a fault. This, however, may result in overlooking actual faults that must be detected.
To correctly adjust design data to measured data that contains slightly displaced edges, there is an idea of developing the design data into pattern data consisting of pixels each being smaller than a sensor pixel. This idea, however, increases the quantity of the pattern data and needs highspeed data processing circuits to elongate a processing time and increase inspection costs.
To cope with the situation that actual photomask pattern has the roundness of corners, the prior art develops design data into binary data and rounds corners in the binary data to approximate the actual photomask patterns. The binary data is made of xe2x80x9c1sxe2x80x9d and xe2x80x9c0sxe2x80x9d and is scanned with a pixel area 20 of FIG. 2B. The pixel area 20 has a central pixel 22 and a radius xe2x80x9cr.xe2x80x9d The value of the central pixel 22 is set to xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d according to a majority of xe2x80x9c1sxe2x80x9d and xe2x80x9c0sxe2x80x9d in the pixel area 20. By determining the value of the central pixel of each pixel area according to a majority, the prior art adjusts corners of the design data to match with those of the actual photomask patterns. The corner-rounded design data serves as reference data. The fault decision circuit 6 compares the reference data with measured pattern data taken from the actual photomask patterns, to see if the photomask patterns have faults. The measured pattern data is obtained by irradiating the photomask patterns with light and by detecting light transmitted through the photomask patterns with a sensor.
The prior art hardly determines a value representing a pattern corner if the size of a sensor pixel is equal to the size of a pattern pixel. More precisely, if an edge of a pattern image crosses the center of a sensor pixel and covers a half of the sensor pixel, the prior art is unable to determine whether it is xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. Namely, the rounding process that is carried out pixel by pixel is incapable of precisely expressing actual photomask patterns. Eventually, the prior art must lower a fault detecting threshold to avoid erroneous detection at the corners of photomask patterns. This leads to overlooking fatal faults that must be detected.
To solve this problem, design data may be developed into binary data whose pixel size is smaller than a sensor pixel, and the binary data is adjusted to match with the roundness of corners of actual photomask patterns, similar to the technique of coping with the slightly displaced edges of photomask patterns. However, making the size of each pixel of the binary data smaller than the size of a sensor pixel increases the quantity of the binary data to raise a problem of needing large-capacity storage devices and high-speed data processing circuits. This technique is unable to completely cope with the corner roundness of actual photomask patterns because the actual corner roundness is irregular depending on corner sizes and types and etching conditions.
In this way, the pattern inspection equipment of the prior art that compares design data used to delineate patterns on a photomask substrate with measured data taken from the delineated actual photomask patterns is unable to adjust the design data to match with the slightly displaced edges of the actual photomask patterns and the minute roundness of the corners of the photomask patterns.
Making the size of a pixel of the developed pattern data smaller than a sensor pixel size to adjust the pattern data to match with the microscopically displaced edges and rounded corners of the actual photomask patterns increases the quantity of the pattern data to raise a need of high-performance computers and high costs.
The prior art is unable to completely adjust the pattern data to the minute edge displacements and corner roundness of the photomask patterns because they are irregular depending on exposing and etching conditions.
An object of the present invention is to solve the problems of the prior art.
More precisely, an object of the present invention is to provide pattern inspection equipment capable of correctly shifting a position of pattern edge and/or correctly rounding a corner of pattern corresponding to the design data that is used to delineate the pattern on an object, thereby adjusting the design data to match with the slightly displaced edges and rounded corners of the delineated actual pattern. These displaced edges and rounded corners are usually caused by pattern manufacturing process such as the etching process of the patterns on the object. Even if a black-and-white boundary of the actual patterns is displaced by a fine distance shorter than the size of a sensor pixel, the present invention is capable of correctly comparing measured data taken from the actual patterns with the design data.
Another object of the present invention is to provide high-speed pattern inspection equipment capable of precisely adjusting design data to match with the minutely displaced edges and rounded corners of actual patterns that have been delineated from the design data, without reducing the sizes of pixels of the design data.
Still another object of the present invention is to provide pattern inspection equipment capable of flexibly coping with the irregularly displaced edges and rounded corners of actual patterns. These irregularities are dependent on the sizes and types of the patterns.
Still another object of the present invention is to provide a pattern inspection method capable of precisely adjusting a position of a pattern edge and roundness at corner in a pattern constructed with design data to match with the minutely displaced edges and rounded corners of actual patterns delineated from the design data. Even if a black-and-white boundary of the patterns is displaced by a distance shorter than the size of a sensor pixel, the pattern inspection method of the present invention is capable of precisely adjusting the design data to compare with the measured data taken from the actual patterns.
Still another object of the present invention is to provide a pattern inspection method capable of flexibly coping with the irregular edge displacements and corner roundness of actual photomask patterns. These irregularities are dependent on the size and type of the patterns.
Still another object of the present invention is to provide a storage medium for storing a pattern inspection program that is capable of precisely adjusting design data to match with measured data taken from actual patterns that have been delineated based on the design data, even if a black-and-white boundary of the patterns is displaced by a distance shorter than the size of a sensor pixel.
Still another object of the present invention is to provide a storage medium for storing a pattern inspection program that is capable of flexibly coping with the irregular edge displacements and corner roundness of patterns that have been delineated on an object based on design patterns. These irregularities are dependent on the sizes and types of the patterns.
In order to accomplish the objects, a first aspect of the present invention comprises a measured data generation unit and a reference data generation unit. The measured data generation unit generates measured data from patterns that have been delineated on a sample according to design data. The measured data may be obtained after detecting light transmitted through or reflected from the patterns formed on the sample such as the photomask substrate, or semiconductor substrate, or LCD substrate, and converting the transmitted or reflected light into digital measured data. The measured data can be obtained by detecting scattered light from the patterns formed on the sample. The reference data generation unit generates reference data used to compare with the measured data to inspect faults in the actual patterns delineated on the sample. This equipment is characterized by the reference data generation unit comprising a multi-valued pattern development circuit and a fine adjustment circuit. The multi-valued pattern development circuit develops the design data into gradational data expressed in multiple gradation levels, and the fine adjustment circuit finely adjusts the pattern edges represented by the gradational data. The number of the xe2x80x9cmultiple gradation levelsxe2x80x9d to express gradational data is a multiple of 4 such as 4, 8, 16, 32, and the like except 2. xe2x80x9cFinely adjusts pattern edgesxe2x80x9d means to finely adjusts position of the pattern edge represented by the pattern data when the black-and-white boundaries (edges) of actual patterns are slightly displaced by a distance smaller than the size of a sensor pixel, or to finely rounding a corner of the pattern represented by the pattern data when the corners of the actual patterns are minutely rounded with dimensions below the size of a sensor pixel.
To finely adjust edges of, or to finely modify sizes of patterns constructed with the design data to match with the measured data, the pattern inspection equipment of the first aspect may have at least the multi-valued pattern development circuit for developing the design data into gradational data expressed in multiple gradation levels, a size modification circuit for shifting the side of the pattern constructed with the gradational data to form the reference data, and a fault decision circuit for comparing the reference data with the measured data. The fault decision circuit compares the measured data with the reference data, and determining whether or not the patterns on the sample have fatal faults. The size modification circuit may modify the gradational data by detecting a maximum value in each specified area in the gradational data to enlarge or to reduce the pattern constructed with the gradational data.
To cope with slight roundness at the corners of the patterns on the sample, the fine adjustment circuit may have a corner rounding circuit for rounding corners in the pattern constructed with the gradational data. The corner rounding circuit may have at least a corner detector for converting the gradational data into binary data and detecting pattern corners based on the binary data. The corner rounding circuit carries out the xe2x80x9crounding processxe2x80x9d on the design data, to cope with a variety of fine changes happening on the actual patterns due to various factors related to pattern manufacturing processes. The first aspect is capable of adjusting the design data to match with the measured data taken from the actual patterns and comparing the adjusted design data with the measured data, to correctly determine whether or not the patterns have fatal faults.
As mentioned above, the pattern inspection equipment of the first aspect is capable of precisely adjusting given design data to match with minute changes in position of edges and roundness of corners on actual patterns formed from the design data so that the adjusted design data may serve as reasonable reference data to be compared with measured data taken from the actual patterns. These small changes in the actual patterns are caused by various reasons related to manufacturing processes of the actual patterns and may sometimes make a pattern edge run across the center of a sensor pixel. Even in such a case, the pattern inspection equipment of the first aspect correctly determines whether or not the patterns are sound without faults. This equipment precisely adjusts the design data to match with the actual patterns without reducing the size of each pixel of the gradational data developed from the design data smaller than a sensor pixel, thereby minimizing an increase in the quantity of the reference data, speeding up the pattern inspection, and reducing the cost of the pattern inspection.
Even if the edges of the actual patterns irregularly change depending on the dimensions and forms of the patterns, the equipment of the first aspect flexibly adjusts the design data to cope with such changes in the actual patterns. The equipment of the first aspect is applicable to a variety of inspection practices.
A second aspect of the present invention provides a pattern inspection method having at least the steps of developing design data into gradational data expressed in multiple gradation levels, finely adjusting edges in the gradational data and generating reference data, generating measured data from actual patterns delineated by using the design data on a sample, and comparing the measured data with the reference data. The number of the xe2x80x9cmultiple gradation levelsxe2x80x9d used to express gradational data is a multiple of 4 and not 2. xe2x80x9cFinely adjusting edgesxe2x80x9d means to finely shift the position of displaced edges or finely rounding the corners of patterns having dimensions less than the size of a sensor pixel.
Instead of shifting the position of edges or rounding corners of pattern constructed with gradational data pixel by pixel, the pattern inspection method of the second aspect finely adjusts them using the multiple gradation levels to cope with slight changes in the edges and corners of actual patterns due to pattern manufacturing processes, thereby improving the practicability of the pattern inspection. Without reducing the size of each pixel of the gradational data smaller than the size of a sensor pixel, the second aspect correctly adjusts the gradational data to match with the actual patterns and quickly complete the pattern inspection. Even if the edges of the actual patterns involve irregular changes depending on the dimensions and forms of the patterns, the second aspect flexibly adjusts the gradational data to match with the actual patterns. Consequently, the pattern inspection method of the second aspect is practical and meets a variety of inspection requirements.
A third aspect of the present invention provides a storage medium readable by computer, for storing a program that executes the pattern inspection method of the second aspect. The program includes at least the steps of developing design data used to delineate patterns on a sample, into gradational data expressed in multiple gradation levels, finely adjusting edges in the gradational data and generating reference data, generating measured data from the delineated actual patterns, and comparing the measured data with the reference data. The storage medium stores the program, which is read by computer so that a central processing unit (CPU) of the computer may execute the program to carry out the pattern inspection method of the second aspect of the present invention. The storage medium may be a semiconductor memory such as a RAM or ROM, a magnetic disk, an optical disk, a magneto-optical disk, a magnetic tape, etc., capable of recording the program.
Stored in the storage medium of the third aspect of the present invention, the program is capable of adjusting pattern data to match with fine changes occurring in actual patterns due to pattern manufacturing processes and coping with a variety of inspection requirements. Similar to the second aspect, the program stored in the storage medium of the third aspect precisely adjusts pattern data to actual patterns without reducing the size of a pixel of gradational data smaller than the size of a sensor pixel. In addition, the program flexibly copes with pattern edges that irregularly change depending on the dimensions and forms of the patterns, thereby meeting a variety of inspection requirements.
Other and further objects and features of the present invention will become obvious upon an understanding of the illustrative embodiments about to be described in connection with the accompanying drawings or will be indicated in the appended claims, and various advantages not referred to herein will occur to one skilled in the art upon employing of the invention in practice.